C - Chemistry – Metallurgy – 22 – C
Patent
C - Chemistry, Metallurgy
22
C
C22C 38/06 (2006.01) C21D 1/18 (2006.01) C21D 8/04 (2006.01) C21D 9/48 (2006.01) C22C 38/02 (2006.01) C21D 1/20 (2006.01)
Patent
CA 2165820
A high-strength steel sheet suitable for deep drawing, characterized by comprising 0.04 to 0.25 mass% of C and 0.3 to 3.0 mass%, in total, of at least one of Si and Al, the steel sheet having multiple phases structure comprising ferrite as a main phase (a phase having the highest volume fraction), not less than 3 vol.% of austenite, and bainite and martensite; said steel satisfying a requirement that a value obtained by dividing volume fraction of Vg (vol.%) of austenite before working by the content of C (mass%) contained in the whole steel, Vg/C, is 40 to 140, a requirement that Vp (volume fraction of austenite at the time of plane strain tensile deformation)/Vs (volume fraction of austenite at the time of shrink flanging deformation) is not more than 0.8, and a requirement represented by the formula 220<Vg{300(2750Cg+600)/(HfVf+HbVb+HmVm)-1}<990 wherein Cg represents the content of C in austenite; Vf represents the volume fraction of ferrite; Hv represents the hardness; Vb represents the volume fraction of bainite; Hb represents the hardness; Vm represents the volume fraction of martensite before working; and Hm represents the hardness. The high-strength steel sheet is produced under specified production conditions of the temperature on the inlet side of rough rolling (hot rolling), annealing conditions in a two-phase region in the step of continuous annealing after cold rolling, cooling conditions, and bainite transformation treatment conditions.
La présente invention concerne une feuille en acier haute résistance convenant à l'emboutissage profond. Sa composition massique est caractérisée par 0,04 % à 0,25 % de carbone et 0,3 % à 3 % de silicium ou d'aluminium. Cet acier, dont la phase principale est le ferrite (c'est à dire la phase prépondérante en volume), est caractérisé par une structure composite comprenant un volume d'au moins 3 % d'austénite, de bainite et de martensite. Cet acier satisfait à 3 conditions. 1~) Vg/C = 40-140, "Vg" étant le pourcentage volumique de l'austénite avant élaboration et "C" étant le pourcentage massique du carbone dans l'acier total; 2~) Vp/Vs ? 0,8, "Vp" étant la proportion volumique de l'austénite en déformation plane avant rupture et "Vs" étant la proportion volumique de l'austénite en déformation de bord rétreint; 3~) 220 < Vg {300(2750Cg+600)/(HfVf+HbVb+HmVm)-1} < 990, "Cg" étant la teneur de l'austénite en carbone, "Hf" étant la dureté du ferrite, "Vf" étant sa proportion volumique, "Hm" étant la dureté de la martensite avant élaboration, et "Vm" étant sa proportion volumique. On produit cette feuille en spécifiant la température du bord d'introduction au laminage à chaud, les conditions de recuit intercritique pour l'opération de recuit continu après laminage à froid, les conditions de refroidissement et les conditions de transformation bainitique.
Hiwatashi Shunji
Kawasaki Kaoru
Koyama Kazuo
Sakuma Yasuharu
Takahashi Manabu
Goudreau Gage Dubuc
Nippon Steel Corporation
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